Adds WmWindow and converts WindowState to use it

ash/wm/common/wm_root_window_controller.h

Index: ash/wm/common/wm_root_window_controller.h
diff --git a/ash/wm/common/wm_root_window_controller.h b/ash/wm/common/wm_root_window_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..358611a8af569cb81a2bab0491ed39f707d8a21c
--- /dev/null
+++ b/ash/wm/common/wm_root_window_controller.h
@@ -0,0 +1,25 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_WM_COMMON_WM_ROOT_CONTROLLER_H_
+#define ASH_WM_COMMON_WM_ROOT_CONTROLLER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+namespace wm {
+
+class WmWindow;
+
+class ASH_EXPORT WmRootWindowController {
+ public:
+  virtual ~WmRootWindowController() {}
+
+  virtual bool HasShelf() = 0;
+};
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_COMMON_WM_ROOT_CONTROLLER_H_